Abstract
Salinity control, nutrient additions, and sediment supply were directly or indirectly the rationale for a $220 million coastal wetland restoration project (Davis Pond River Diversion) that began in 2002. We sampled Mississippi River water going in and out of the receiving basin from 1999 to 2018 to understand why wetland loss increased after it began. There was a reduction in inorganic sediments, nitrogen (N), and phosphorus (P) concentrations within the ponding area of 77%, 39% and 34%, respectively, which is similar to that in other wetlands. But the average sediment accumulation of 0.6 mm year−1 inadequately balances the present-day 5.6 mm year−1 sea level rise or the 7.9 ± 0.13 mm year−1 accretion rates in these organic soils. Nutrients added likely reduced live belowground biomass and soil strength, and increased decomposition of the organic matter necessary to sustain elevations. The eutrophication of the downstream aquatic system from the diversion, principally by P additions, increased Chl a concentrations to a category of ‘poor’ water quality. We conclude that this diversion, if continued, will be a negative influence on wetland area and will eutrophy the estuary. It is a case history example for understanding the potential effects arising from proposed river diversions.
Highlights
Humans have changed coastal landscapes as they moved some or all of a river’s flow across landscapes throughout human histories for a variety of reasons
The concentration of ammonium did not decline in the Lake Cataoutche or in Lake Salvador but did decline in the Couba Island passes (Fig. 4c), whereas ammonium concentrations declined in Lake Cataoutche but not in Lake Salvador or Couba Island passes (Fig. 4d)
The N and P loading rates and removal rates are within the ranges stated in a review of the scientific literature by Land et al (2016; Table 1)
Summary
Humans have changed coastal landscapes as they moved some or all of a river’s flow across landscapes throughout human histories for a variety of reasons. The dikes of the Yellow River, for example, were breached in 1128 CE for military reasons, and the resulting river avulsion captured the nearby Huai river, which later became blocked; the Yellow river soon debouched to the south of the Shandong Peninsula and into the Yellow Sea. Agricultural expansion in England’s Wash began in the late 1500’s and led to re-direction of numerous river flows (Ash, 2017). The Everglades ecosystem is riddled with water re-direction around, into and out of wetlands that have changed under various political pressures. Eighty-eight percent of the Santee River (Charleston, SC) was redirected into the Cooper River in 1941 to develop hydroelectricity, only to have part of it redirected back by 1975 because of shoaling in Charleston Harbor (Bradley et al, 1990)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call